2001 Galant service engine light on & won't stay running/ runs rough

HI,
I have a 2001 Galant 3.0 V6 that I just did a tune-up on, & replaced the radiator, hoses & thermostat, now the service engine light stays on, it runs rough & dies. When it was cold, right after parts were replaced, it started right up, but ran rough, then once warm, it dies unless given gas. Tune-up consisted of plugs, wires, cap, rotor, PCV. Parts were taken off one at a time & replaced so wires wouldn't get mixed up. I'm thinking a bad sensor, but which one, where is the port to plug in a sensor tester & how do I get the codes? What should the intake plenum bolts be torqued to?
Thanks.
Bill

This probably happened because the battery was disconnected. If this is the case then your car’s computer chip needs to calibrate the engine’s RPM. The same thing happened to me few years ago after I replaced my spark plugs and battery, at the beginning I thought that I screw up something, so I called the Mitsubishi dealership and they told to do the following (my memory is a little rusty but I think it went this way):
1-Disconnect the battery and wait for few minutes then reconnect it.
2-turn the car on and keep it running for 15 minutes (don’t bush the gas or change gears) while its running turn on all the electrical elements in your (radio, AC, hedlights..etc).
3- after 15 minutes change the gear to D move the car forward then change the gear to R and move it backward, you’re done.
Note: I’m not sure about step 3 so if this doesn’t work, start over ,do steps 1 and 2, and change step 3:A-Instead of moving the car just change the gear to D, R, L3, L2, L1, and then back to P, and turn the car off.B-If this also doesn’t work, don’t do step three at all and instead just turn the car off after 15 minutes.
If none of this works, then I guess you need to call the Mitsubishi dealer guys and ask them nicely what the right procedure is. good luck.

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Robert, have vehicle scanned for diagnostic codes. Check for vacuum leaks and if you have not done recently give vehicle a complete tune up cap,rottor,wires,plugs,filter's,etc, including injector/throttle body cleaning. Check the attached links,instruction and guides, Good luck
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2. A tune up should have shown a problem if one existed with the ignition.

3. You have a bad fuel injector.

you can unplug the fuel injector at cylinder #2, run the engine and see if the problem stays the same or gets worse. If it stays the same then the injector is bad, or the wires/harness to the injector are bad.

thats the risk you run when you have a third party not liscensed by volkswagen mess with your ECM. take it to the tuning shop that did the remap work and ask them to redo it because it messed your engine up, if you make a big enough stink they might do it for free.